The unusual tusks—found on the outside of the male's mouth—have baffled scientists because they are not used for capturing prey, said study co-author Scott Baker, associate director of the Marine Mammal Institute at Oregon State University.

"Up until now, the purpose of the beaked whale tusks has been mysterious," he added.

Beaked whales and the narwhal are the only cetacean species with tusks, according to Baker. Cetaceans are marine mammals such as whales and dolphins. In the narwhal the single unicorn-like tusk is a modified upper tooth, whereas the paired tusks of the beaked whales are modified lower teeth.

After using DNA samples to reconstruct the evolutionary relationships of 13 of the 14 known beaked whale species, Baker and lead author Merel Dalebout of the University of New South Wales, Australia, said the tusks may help females identify male members of their own species to mate with.

The findings are published in the December issue of the journal Systematic Biology

Family Dynamics

Existing beaked whale populations are found in nearly every ocean. Dalebout and Baker have discovering new species as recently as 2002.

These rare whales are mysterious, because they spend much of their time at great depths searching for food—primarily squid, which the whales suck up like a vacuum cleaners.

"There are several beaked whale species that are still known from only a handful of specimens (strandings) and some have never been seen alive," Dalebout said via email.

Robert Pitman, a marine biologist with NOAA, was not part of the tusk research but recently studied what may be a new beaked-whale species near Palmyra Island in the Pacific Ocean.